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<tr class="t-nv-h2"><td colspan="5"> 概述 </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="value_category.html" title="cpp/language/value category"> 值类别</a>（左值 lvalue、右值 rvalue、亡值 xvalue）</td></tr>
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<tr class="t-nv-h2"><td colspan="5"> 运算符 </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_assignment.html" title="cpp/language/operator assignment"> 赋值运算符</a>:
<code>a=b</code>, <code>a+=b</code>, <code>a-=b</code>, <code>a*=b</code>, <code>a/=b</code>, <code>a%=b</code>, <code>a&amp;=b</code>, <code>a|=b</code>, <code>a^=b</code>, <code>a&lt;&lt;=b</code>, <code>a&gt;&gt;=b</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_incdec.html" title="cpp/language/operator incdec"> 自增与自减</a>: <code>++a</code>, <code>--a</code>, <code>a++</code>, <code>a--</code></td></tr>
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<code>+a</code>, <code>-a</code>, <code>a+b</code>, <code>a-b</code>, <code>a*b</code>, <code>a/b</code>, <code>a%b</code>, <code>~a</code>, <code>a&amp;b</code>, <code>a|b</code>, <code>a^b</code>, <code>a&lt;&lt;b</code>, <code>a&gt;&gt;b</code> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_logical.html" title="cpp/language/operator logical"> 逻辑运算符</a>: <code>a||b</code>, <code>a&amp;&amp;b</code>, <code>!a</code></td></tr>
<tr class="t-nv"><td colspan="5"> <strong class="selflink"> 比较运算符</strong>: <code>a==b</code>, <code>a!=b</code>, <code>a&lt;b</code>, <code>a&gt;b</code>, <code>a&lt;=b</code>, <code>a&gt;=b</code>, <code>a&lt;=&gt;b</code><span class="t-mark-rev t-since-cxx20">(C++20)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_member_access.html" title="cpp/language/operator member access"> 成员访问运算符</a>: <code>a[b]</code>, <code>*a</code>, <code>&amp;a</code>, <code>a-&gt;b</code>, <code>a.b</code>, <code>a-&gt;*b</code>, <code>a.*b</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_other.html" title="cpp/language/operator other"> 其他运算符</a>: <code>a(...)</code>, <code>a,b</code>, <code>a?b:c</code> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="default_comparisons.html" title="cpp/language/default comparisons">默认比较</a><span class="t-mark-rev t-since-cxx20">(C++20)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_alternative.html" title="cpp/language/operator alternative">运算符的代用表示</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_precedence.html" title="cpp/language/operator precedence">优先级和结合性</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="fold.html" title="cpp/language/fold">折叠表达式</a><span class="t-mark-rev t-since-cxx17">(C++17)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="new.html" title="cpp/language/new">new 表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="delete.html" title="cpp/language/delete">delete 表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="throw.html" title="cpp/language/throw">throw 表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="alignof.html" title="cpp/language/alignof">alignof</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="sizeof.html" title="cpp/language/sizeof">sizeof</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="sizeof....html" title="cpp/language/sizeof...">sizeof...</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="typeid.html" title="cpp/language/typeid">typeid</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="noexcept.html" title="cpp/language/noexcept">noexcept</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operators.html" title="cpp/language/operators">运算符重载</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> 类型转换 </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="implicit_cast.html" title="cpp/language/implicit conversion">隐式转换</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="const_cast.html" title="cpp/language/const cast">const_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="static_cast.html" title="cpp/language/static cast">static_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="reinterpret_cast.html" title="cpp/language/reinterpret cast">reinterpret_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="dynamic_cast.html" title="cpp/language/dynamic cast">dynamic_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="explicit_cast.html" title="cpp/language/explicit cast">显式转换</a> <code>(T)a</code>, <code>T(a)</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="cast_operator.html" title="cpp/language/cast operator">用户定义转换</a></td></tr>
</table></div>
</div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>比较参数。
</p>
<table class="wikitable" style="font-size:85%;">

<tr>
<th rowspan="2">运算符名
</th>
<th rowspan="2">语法
</th>
<th rowspan="2"><a href="operators.html" title="cpp/language/operators">可重载</a>
</th>
<th colspan="2">原型示例（对 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> T</span></span>）
</th></tr>
<tr>
<th>作为成员函数
</th>
<th>作为自由（命名空间）函数
</th></tr>
<tr>
<td>等于
</td>
<td> <code>a == b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator <span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> T <span class="sy3">&amp;</span>a, <span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td>不等于
</td>
<td> <code>a != b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator <span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T <span class="sy3">&amp;</span>a, <span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td>小于
</td>
<td> <code>a &lt; b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy1">&lt;</span><span class="br0">(</span><span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator <span class="sy1">&lt;</span><span class="br0">(</span><span class="kw4">const</span> T <span class="sy3">&amp;</span>a, <span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td>大于
</td>
<td> <code>a &gt; b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy1">&gt;</span><span class="br0">(</span><span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator <span class="sy1">&gt;</span><span class="br0">(</span><span class="kw4">const</span> T <span class="sy3">&amp;</span>a, <span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td>小于或等于
</td>
<td> <code>a &lt;= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy1">&lt;=</span><span class="br0">(</span><span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator <span class="sy1">&lt;=</span><span class="br0">(</span><span class="kw4">const</span> T <span class="sy3">&amp;</span>a, <span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td>大于或等于
</td>
<td> <code>a &gt;= b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy1">&gt;=</span><span class="br0">(</span><span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator <span class="sy1">&gt;=</span><span class="br0">(</span><span class="kw4">const</span> T <span class="sy3">&amp;</span>a, <span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td>三路比较<span class="t-mark-rev t-since-cxx20">(C++20)</span>
</td>
<td> <code>a &lt;=&gt; b</code>
</td>
<td style="background: #90ff90; color: black; vertical-align: middle; text-align: center;" class="table-yes">是
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*见说明*/</span> T<span class="sy4">::</span><span class="me2">operator</span> <span class="sy1">&lt;=&gt;</span><span class="br0">(</span><span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*见说明*/</span> operator <span class="sy1">&lt;=&gt;</span><span class="br0">(</span><span class="kw4">const</span> T <span class="sy3">&amp;</span>a, <span class="kw4">const</span> T2 <span class="sy3">&amp;</span>b<span class="br0">)</span><span class="sy4">;</span></span></span>
</td></tr>
<tr>
<td colspan="5">
<dl><dd><b>注解</b><br>
</dd></dl>
<ul><li> 内建运算符若返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span>，则大多数<a href="operators.html" title="cpp/language/operators">用户定义重载</a>亦返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span>，使得用户定义运算符能以与内建运算符相同的方式使用。然而，在用户定义运算符重载中，任何类型都可用作返回类型（包含 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span>）。
</li><li> <code>T2</code> 可以是包括 <code>T</code> 在内的任何类型
</li></ul>
</td></tr></table>
<h3><span class="mw-headline" id=".E5.8F.8C.E8.B7.AF.E6.AF.94.E8.BE.83">双路比较</span></h3>
<p>双路比较运算符表达式的形式为
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>&lt;</b></code> <span class="t-spar">rhs</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>&gt;</b></code> <span class="t-spar">rhs</span>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>&lt;=</b></code> <span class="t-spar">rhs</span>
</td>
<td> (3)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>&gt;=</b></code> <span class="t-spar">rhs</span>
</td>
<td> (4)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>==</b></code> <span class="t-spar">rhs</span>
</td>
<td> (5)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>!=</b></code> <span class="t-spar">rhs</span>
</td>
<td> (6)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<div class="t-li1"><span class="t-li">1)</span> 若 <span class="t-spar">lhs</span> 小于 <span class="t-spar">rhs</span> 则返回 <code>true</code>，否则返回 <code>false</code>。</div>
<div class="t-li1"><span class="t-li">2)</span> 若 <span class="t-spar">lhs</span> 大于 <span class="t-spar">rhs</span> 则返回 <code>true</code>，否则返回 <code>false</code>。</div>
<div class="t-li1"><span class="t-li">3)</span> 若 <span class="t-spar">lhs</span> 小于或等于 <span class="t-spar">rhs</span> 则返回 <code>true</code>，否则返回 <code>false</code>。</div>
<div class="t-li1"><span class="t-li">4)</span> 若 <span class="t-spar">lhs</span> 大于或等于 <span class="t-spar">rhs</span> 则返回 <code>true</code>，否则返回 <code>false</code>。</div>
<div class="t-li1"><span class="t-li">5)</span> 若 <span class="t-spar">lhs</span> 等于 <span class="t-spar">rhs</span> 则返回 <code>true</code>，否则返回 <code>false</code>。</div>
<div class="t-li1"><span class="t-li">6)</span> 若 <span class="t-spar">lhs</span> 不等于 <span class="t-spar">rhs</span> 则返回 <code>true</code>，否则返回 <code>false</code>。</div>
<p>所有情况下，对于内建运算符，<span class="t-spar">lhs</span> 和 <span class="t-spar">rhs</span> 在应用<a href="implicit_cast.html#.E5.B7.A6.E5.80.BC.E5.88.B0.E5.8F.B3.E5.80.BC.E8.BD.AC.E6.8D.A2" title="cpp/language/implicit conversion">左值到右值</a>、<a href="implicit_cast.html#.E6.95.B0.E7.BB.84.E5.88.B0.E6.8C.87.E9.92.88.E8.BD.AC.E6.8D.A2" title="cpp/language/implicit conversion">数组到指针</a>和<a href="implicit_cast.html#.E5.87.BD.E6.95.B0.E5.88.B0.E6.8C.87.E9.92.88.E8.BD.AC.E6.8D.A2" title="cpp/language/implicit conversion">函数到指针</a>标准转换后，必须具有下列类型之一
</p>
<ul><li> 算术或枚举类型（见下文的算术比较运算符）
</li><li> 指针类型（见下文的指针比较运算符）
</li></ul>
<p><span class="t-rev-inl t-since-cxx20"><span>若两个运算数在应用这些转换前均具有数组类型，则这种比较被弃用。</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>
</p><p>任何情况下，结果均为 <code>bool</code> 纯右值。
</p>
<h4><span class="mw-headline" id=".E7.AE.97.E6.9C.AF.E6.AF.94.E8.BE.83.E8.BF.90.E7.AE.97.E7.AC.A6">算术比较运算符</span></h4>
<p>如果两个操作数具有算术或（有作用域或无作用域）枚举类型，则遵循<a href="operator_arithmetic.html" title="cpp/language/operator arithmetic">算术运算符</a>的规则，对两个操作数实施<i>一般算术转换</i>。转换之后进行值的比较：
</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <a href="../io/manip/boolalpha.html"><span class="kw1764">std::<span class="me2">boolalpha</span></span></a><span class="sy4">;</span>
    <span class="kw4">int</span> n <span class="sy1">=</span> <span class="sy2">-</span><span class="nu0">1</span><span class="sy4">;</span>
 
    <span class="kw4">int</span> n2 <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">" -1 == 1? "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>n <span class="sy1">==</span> n2<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">"Comparing two signed values:<span class="es1">\n</span>"</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">" -1  &lt; 1? "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>n <span class="sy1">&lt;</span> n2<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">" -1  &gt; 1? "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>n <span class="sy1">&gt;</span> n2<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
 
    <span class="kw4">unsigned</span> <span class="kw4">int</span> u <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"Comparing signed and unsigned:<span class="es1">\n</span>"</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">" -1  &lt; 1? "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>n <span class="sy1">&lt;</span> u<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">" -1  &gt; 1? "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>n <span class="sy1">&gt;</span> u<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
 
    <span class="kw4">unsigned</span> <span class="kw4">char</span> uc <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"Comparing signed and smaller unsigned:<span class="es1">\n</span>"</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">" -1  &lt; 1? "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>n <span class="sy1">&lt;</span> uc<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">" -1  &gt; 1? "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>n <span class="sy1">&gt;</span> uc<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">
 -1 == 1? false
Comparing two signed values:
 -1  &lt; 1? true
 -1  &gt; 1? false
Comparing signed and unsigned:
 -1  &lt; 1? false
 -1  &gt; 1? true
Comparing signed and smaller unsigned:
 -1  &lt; 1? true
 -1  &gt; 1? false</pre></div></div> 
</div>
<h4><span class="mw-headline" id=".E6.8C.87.E9.92.88.E6.AF.94.E8.BE.83.E8.BF.90.E7.AE.97.E7.AC.A6">指针比较运算符</span></h4>
<p>比较运算符可用于比较二个指针（或成员指针，但仅对于 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">==</span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy3">!</span><span class="sy1">=</span></span></span>），或一个<span class="t-rev-inl t-since-cxx14"><span>（成员）</span> <span><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></span></span>指针和一个空指针常量<span class="t-rev-inl t-until-cxx14"><span>，或两个空指针常量（但要至少一个为 <span class="t-lc"><a href="../types/nullptr_t.html" title="cpp/types/nullptr t">std::nullptr_t</a></span>：NULL 和 NULL 的比较遵循算术比较规则）</span> <span><span class="t-mark-rev t-until-cxx14">(C++14 前)</span></span></span>。
</p><p>首先，对两个操作数应用<a href="implicit_cast.html" title="cpp/language/implicit conversion">指针转换</a>（若参数为成员指针则为成员指针转换）<span class="t-rev-inl t-since-cxx17"><span>、函数指针转换</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span>和<a href="implicit_cast.html" title="cpp/language/implicit conversion">限定性转换</a>，以获得<i>合成指针类型</i>，规则如下
</p>
<div class="t-li1"><span class="t-li">1)</span> 若两个操作数均为空指针常量，则合成指针类型为 <span class="t-lc"><a href="../types/nullptr_t.html" title="cpp/types/nullptr t">std::nullptr_t</a></span></div>
<div class="t-li1"><span class="t-li">2)</span> 若一个操作数为空指针常量，而另一个为指针，则合成类型正是该指针类型</div>
<div class="t-li1"><span class="t-li">3)</span> 若一个操作数为指向 <i>cv1</i> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 的指针，而另一个为（对于某类型 <code>T</code>）指向 <i>cv2</i> <code>T</code> 的指针，其中 <code>T</code> 为对象类型或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span>，则合成类型为“指向 <i>cv12</i> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 的指针”，其中 <i>cv12</i> 为 <i>cv1</i> 与 <i>cv2</i> 的合并</div>
 <table class="t-rev-begin">
<tr class="t-rev t-until-cxx14"><td>
<div class="t-li1"><span class="t-li">4)</span> 若两个操作数均为指向带有不同 cv 限定的同一类型的指针，则合成类型为指向同一类型的指针并带有两个实参 cv 限定性的合并 cv 限定性。
</div></td>
<td><span class="t-mark-rev t-until-cxx14">(C++14 前)</span></td></tr>
<tr class="t-rev t-since-cxx14"><td>
<div class="t-li1"><span class="t-li">4)</span> 若操作数的类型分别为指向（可能 cv 限定）T1 的指针 P1，和指向（可能 cv 限定）T2 的指针 P2，且若 T1 与 T2 相同或是 T2 的基类，则合成指针类型为 P1 与 P2 的 <i>cv 结合</i>类型。否则，若 T2 为 T1 的基类，则合成指针类型为 P2 与 P1 的 <i>cv 结合</i>类型。</div>
<div class="t-li1"><span class="t-li">5)</span> 若操作数的类型分别为指向（可能 cv 限定）U1 类型的 T1 的成员指针，和指向（可能 cv 限定）U2 类型的 T2 的成员指针，且若 T1 与 T2 相同或派生于 T2，则合成指针类型为 MP1 和 MP2 的 <i>cv 结合</i>类型。否则，若 T2 派生于 T1，则合成指针类型为 MP2 与 MP1 的 <i>cv 结合</i>类型。</div>
<div class="t-li1"><span class="t-li">6)</span> 若操作数 P1 和 P2 的类型具有相同层数的多层混合指针和成员指针类型，而仅在任何层上的 cv 限定性有别，则合成指针类型为 P1 与 P2 的 <i>cv 结合</i>类型</div>
<p>上面的定义中，两个指针类型 P1 和 P2 的 <i>cv 结合</i>类型，是拥有相同的层数且每层具有与 P1 相同类型的类型 P3，其中每层上的 cv 限定性设定如下：
</p>
<div class="t-li1"><span class="t-li">a)</span> 除顶层之外的每层，其 cv 限定性为该层上 P1 与 P2 的 cv 限定性的合并</div>
<div class="t-li1"><span class="t-li">b)</span> 如果有任何层上得到的 cv 限定性与同一层上 P1 或 P2 的 cv 限定性不同，则对顶层和此层之间的每一层添加 const。</div>
<p>例如，<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">int</span><span class="sy2">*</span></span></span> 的合成指针类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span></span></span>。<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span><span class="sy2">**</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">int</span><span class="sy2">**</span></span></span> 的合成指针类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">int</span><span class="sy2">*</span> <span class="kw4">const</span><span class="sy2">*</span></span></span>。注意，C++14 之前无法比较 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span><span class="sy2">**</span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="kw4">int</span><span class="sy2">**</span></span></span>。
</p>
</td>
<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td></tr>
<tr class="t-rev t-since-cxx17"><td>
<p>除上述之外，函数指针和指向 noexcept 函数的指针（只要函数类型相同）的合成指针类型为函数指针。
</p>
</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td></tr>
</table>
<p>注意这意味着任何指针都能与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 进行比较。
</p><p>两个对象指针（转换后）的比较结果定义如下：
</p>
<div class="t-li1"><span class="t-li">1)</span> 若两个指针指向同一数组的不同元素，或同一数组的不同元素内的子对象，则指向拥有较高下标的元素的指针<i>比较大于</i>另一指针。换言之，比较指针的结果与比较其所指向的元素下标结果相同。</div>
<div class="t-li1"><span class="t-li">2)</span> 若一个指针指向数组元素，或数组元素的子对象，而另一指针指向数组末尾元素后一位置，则后者<i>比较大于</i>前者。<span class="t-rev-inl t-since-cxx17"><span>指向单个对象的指针被当做指向单元素数组的指针：<code>&amp;obj+1</code> 比较大于 <code>&amp;obj</code>。</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span></div>
<div class="t-li1"><span class="t-li">3)</span> 若在非联合体类类型的对象内，两个指针指向拥有相同<a href="access.html" title="cpp/language/access">成员访问</a>的不同非静态数据成员，或（递归地）指向这种成员的子对象或数组元素，则指向较后声明的成员的指针<i>比较大于</i>另一指针。换言之，三个成员访问模式的每一者中的类成员按声明顺序置于内存中。</div>
<p>两个（转换后）指针的相等性比较的结果定义如下：
</p>
<div class="t-li1"><span class="t-li">1)</span> 若两个指针均为空指针值，则它们<i>比较相等</i></div>
<div class="t-li1"><span class="t-li">2)</span> 若两个指针均为函数指针且指向同一函数，则它们<i>比较相等</i></div>
<div class="t-li1"><span class="t-li">3)</span> 若两个指针均为对象指针且表示相同地址，则它们<i>比较相等</i>（这包括两个指向同一联合体的不同非静态成员的指针，指向标准布局结构体与其首成员的指针，由 reinterpret_cast 关联的指针等）</div>
<div class="t-li1"><span class="t-li">4)</span> 所有其他指针的比较不相等。</div>
<p>两个（转换后）成员指针的比较结果定义如下：
</p>
<div class="t-li1"><span class="t-li">1)</span> 若两个成员指针均为空成员指针值，则它们<i>比较相等</i>。</div>
<div class="t-li1"><span class="t-li">2)</span> 否则，若两个成员指针之一为空成员指针值，则它们比较不相等。</div>
<div class="t-li1"><span class="t-li">3)</span> 否则，若其中之一为指向虚成员函数的指针，则结果未指明。</div>
<div class="t-li1"><span class="t-li">4)</span> 否则，当且仅当以一个其关联类类型的假想对象对它们解引用时，它们会指代同一最终派生对象或同一子对象的相同成员，两个成员指针相等。</div>
<div class="t-li1"><span class="t-li">5)</span> 否则它们的比较不相等。</div>
<p>若指针 <code>p</code> <i>比较等于</i>指针 <code>q</code>，则 <code>p&lt;=q</code> 和 <code>p&gt;=q</code> 都产出 <code>true</code> 而 <code>p&lt;q</code> 和 <code>p&gt;q</code> 都产出 <code>false</code>。
</p><p>若指针 <code>p</code> <i>比较大于</i>指针 <code>q</code>，则 <code>p&gt;=q</code>、<code>p&gt;q</code>、<code>q&lt;=p</code> 和 <code>q&lt;p</code> 都产出 <code>true</code> 而 <code>p&lt;=q</code>、<code>p&lt;q</code>、<code>q&gt;=p</code> 和 <code>q&gt;p</code> 都产出 <code>false</code>。
</p><p>若未指明两个指针的比较大于或比较相等，则其比较结果未指明。其结果可以是不确定的，并且甚至不必在程序的同一次执行中，在拥有相同操作数的相同表达式的多次求值之间保持一致：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">int</span> x, y<span class="sy4">;</span>
 
<span class="kw4">bool</span> f<span class="br0">(</span><span class="kw4">int</span><span class="sy2">*</span> p, <span class="kw4">int</span><span class="sy2">*</span> q<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> p <span class="sy1">&lt;</span> q<span class="sy4">;</span> <span class="br0">}</span>
 
<a href="../error/assert.html"><span class="kw774">assert</span></a><span class="br0">(</span>f<span class="br0">(</span><span class="sy3">&amp;</span>x, <span class="sy3">&amp;</span>y<span class="br0">)</span> <span class="sy1">==</span> f<span class="br0">(</span><span class="sy3">&amp;</span>x, <span class="sy3">&amp;</span>y<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 在遵从标准的实现中可能引发断言</span></pre></div></div>
<p>在<a href="overload_resolution.html#.E8.B0.83.E7.94.A8.E9.87.8D.E8.BD.BD.E8.BF.90.E7.AE.97.E7.AC.A6" title="cpp/language/overload resolution">针对用户定义运算符的重载决议</a>中，对于（包括枚举类型的）每个提升后算术类型 L 和 R，下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">&lt;</span><span class="br0">(</span>L, R<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">&gt;</span><span class="br0">(</span>L, R<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">&lt;=</span><span class="br0">(</span>L, R<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">&gt;=</span><span class="br0">(</span>L, R<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span>L, R<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span>L, R<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>对于每个对象指针或函数指针<span class="t-rev-inl t-until-cxx14"><span>或 <span class="t-lc"><a href="../types/nullptr_t.html" title="cpp/types/nullptr t">std::nullptr_t</a></span> </span> <span><span class="t-mark-rev t-until-cxx14">(C++14 前)</span></span></span>的类型 <code>P</code>，下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">&lt;</span><span class="br0">(</span>P, P<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">&gt;</span><span class="br0">(</span>P, P<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">&lt;=</span><span class="br0">(</span>P, P<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">&gt;=</span><span class="br0">(</span>P, P<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span>P, P<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span>P, P<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>对于每个为成员对象指针或成员函数指针或 <span class="t-lc"><a href="../types/nullptr_t.html" title="cpp/types/nullptr t">std::nullptr_t</a></span> 的类型 <code>MP</code>，下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span>MP, MP<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span>MP, MP<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B_2">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="kw1">struct</span> Foo  <span class="br0">{</span> <span class="kw4">int</span> n1<span class="sy4">;</span> <span class="kw4">int</span> n2<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">union</span> Union <span class="br0">{</span> <span class="kw4">int</span> n<span class="sy4">;</span> <span class="kw4">double</span> d<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <a href="../io/manip/boolalpha.html"><span class="kw1764">std::<span class="me2">boolalpha</span></span></a><span class="sy4">;</span>
 
    <span class="kw4">char</span> a<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"abc"</span><span class="sy4">;</span>
 
    <span class="kw4">char</span><span class="sy2">*</span> p1 <span class="sy1">=</span> <span class="sy3">&amp;</span>a<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span><span class="sy4">;</span>
    <span class="kw4">char</span><span class="sy2">*</span> p2 <span class="sy1">=</span> <span class="sy3">&amp;</span>a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"Pointers to array elements: p1 == p2 "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>p1 <span class="sy1">==</span> p2<span class="br0">)</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">", p1 &lt; p2 "</span>  <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>p1 <span class="sy1">&lt;</span> p2<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
 
    Foo f<span class="sy4">;</span>
    <span class="kw4">int</span><span class="sy2">*</span> p3 <span class="sy1">=</span> <span class="sy3">&amp;</span>f.<span class="me1">n1</span><span class="sy4">;</span>
    <span class="kw4">int</span><span class="sy2">*</span> p4 <span class="sy1">=</span> <span class="sy3">&amp;</span>f.<span class="me1">n2</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"Pointers to members of a class: p3 == p4 "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>p3 <span class="sy1">==</span> p4<span class="br0">)</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">", p3 &lt; p4 "</span>  <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>p3 <span class="sy1">&lt;</span> p4<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
 
    Union u<span class="sy4">;</span>
    <span class="kw4">int</span><span class="sy2">*</span> p5 <span class="sy1">=</span> <span class="sy3">&amp;</span>u.<span class="me1">n</span><span class="sy4">;</span>
    <span class="kw4">double</span><span class="sy2">*</span> p6 <span class="sy1">=</span> <span class="sy3">&amp;</span>u.<span class="me1">d</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"Pointers to members of a union: p5 == (void*)p6 "</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>p5 <span class="sy1">==</span> <span class="br0">(</span><span class="kw4">void</span><span class="sy2">*</span><span class="br0">)</span>p6<span class="br0">)</span>
              <span class="sy1">&lt;&lt;</span> <span class="st0">", p5 &lt; p6 "</span>  <span class="sy1">&lt;&lt;</span> <span class="br0">(</span>p5 <span class="sy1">&lt;</span> <span class="br0">(</span><span class="kw4">void</span><span class="sy2">*</span><span class="br0">)</span>p6<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">Pointers to array elements: p1 == p2 false, p1 &lt; p2 true
Pointers to members of a class: p3 == p4 false, p3 &lt; p4 true
Pointers to members of a union: p5 == (void*)p6 true, p5 &lt; p6 false</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
<p>因为这些运算符从左到右组合，故表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="sy1">&lt;</span>b<span class="sy1">&lt;</span>c</span></span> 被分析为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a<span class="sy1">&lt;</span>b<span class="br0">)</span><span class="sy1">&lt;</span>c</span></span>，而非 <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="sy1">&lt;</span><span class="br0">(</span>b<span class="sy1">&lt;</span>c<span class="br0">)</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a<span class="sy1">&lt;</span>b<span class="br0">)</span><span class="sy3">&amp;&amp;</span><span class="br0">(</span>b<span class="sy1">&lt;</span>c<span class="br0">)</span></span></span>。
</p><p>对<a href="operators.html#.E5.85.B3.E7.B3.BB.E8.BF.90.E7.AE.97.E7.AC.A6" title="cpp/language/operators">用户定义的 operator&lt;</a> 的一项常见要求是<a href="https://en.wikipedia.org/wiki/Strict_weak_ordering" class="extiw" title="enwiki:Strict weak ordering">严格弱序</a>。尤其是，用<a href="../named_req/Compare.html" title="cpp/named req/Compare"><i>比较</i> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Compare)</span> </a>类型进行工作的标准算法和容器如 <span class="t-lc"><a href="../algorithm/sort.html" title="cpp/algorithm/sort">std::sort</a></span>、<span class="t-lc"><a href="../algorithm/max_element.html" title="cpp/algorithm/max element">std::max_element</a></span>、<span class="t-lc"><a href="../container/map.html" title="cpp/container/map">std::map</a></span> 等都对此有所要求。
</p><p>尽管未指明对随机来源（例如不都指向同一数组中的成员）的指针比较的结果，许多实现都提供指针的<a href="https://en.wikipedia.org/wiki/Total_order#Strict_total_order" class="extiw" title="enwiki:Total order">严格全序</a>，例如若它们被实现为连续的虚拟地址空间中的地址。不这样做的实现（例如并非指针的所有位都是内存地址的一部分而在比较中必须被忽略，或要求进行额外的计算否则指针与整数并非 1 对 1 关系），要为指针提供具有这项保证的 <span class="t-lc"><a href="../utility/functional/less.html" title="cpp/utility/functional/less">std::less</a></span> 的特化。这使得程序可以将随机来源的所有指针都用作标准关联容器（如 <span class="t-lc"><a href="../container/set.html" title="cpp/container/set">std::set</a></span> 或 <span class="t-lc"><a href="../container/map.html" title="cpp/container/map">std::map</a></span>）的键。
</p><p>对于既<a href="../named_req/EqualityComparable.html" title="cpp/named req/EqualityComparable"><i>可相等比较</i> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(EqualityComparable)</span> </a>又<a href="../named_req/LessThanComparable.html" title="cpp/named req/LessThanComparable"><i>可小于比较</i> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LessThanComparable)</span> </a>的类型，C++ 标准库在<i>相等</i>（即表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">==</span> b</span></span> 的值），和<i>等价</i>（即表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span><span class="br0">(</span>a <span class="sy1">&lt;</span> b<span class="br0">)</span> <span class="sy3">&amp;&amp;</span> <span class="sy3">!</span><span class="br0">(</span>b <span class="sy1">&lt;</span> a<span class="br0">)</span></span></span> 的值）之间做出区别。
</p><p>C++14 中移除了指针与空指针常量间的比较。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">char</span> <span class="sy2">*</span> p<span class="br0">)</span>
<span class="br0">{</span>
  <span class="kw1">if</span> <span class="br0">(</span>p <span class="sy1">&gt;</span> <span class="nu0">0</span><span class="br0">)</span> <span class="br0">{</span> ... <span class="br0">}</span> <span class="co1">// C++98..C++11 中 OK，C++14 中不能编译</span>
  <span class="kw1">if</span> <span class="br0">(</span>p <span class="sy1">&gt;</span> nullptr<span class="br0">)</span> <span class="br0">{</span> ... <span class="br0">}</span> <span class="co1">// C++11 中 OK，C++14 中不能编译</span>
<span class="br0">}</span></pre></div></div>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx20"><td>
<h3> <span class="mw-headline" id=".E4.B8.89.E8.B7.AF.E6.AF.94.E8.BE.83">三路比较</span></h3>
<p>三路比较运算符表达式的形式为
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">lhs</span> <code><b>&lt;=&gt;</b></code> <span class="t-spar">rhs</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>表达式返回一个对象，使得
</p>
<ul><li> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">lhs <span class="sy1">&lt;</span> rhs</span></span> 则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy1">&lt;=&gt;</span> b<span class="br0">)</span> <span class="sy1">&lt;</span> <span class="nu0">0</span></span></span>
</li><li> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">lhs <span class="sy1">&gt;</span> rhs</span></span> 则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy1">&lt;=&gt;</span> b<span class="br0">)</span> <span class="sy1">&gt;</span> <span class="nu0">0</span></span></span>
</li><li> 而若 <span class="t-c"><span class="mw-geshi cpp source-cpp">lhs</span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">rhs</span></span> 相等/等价则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>a <span class="sy1">&lt;=&gt;</span> b<span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span></span></span>。
</li></ul>
<p>如果操作数之一为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> 类型而另一个不是，程序非良构。
</p><p>若两个操作数均具有算术类型，或若一个具有无作用域枚举类型而另一个具有整型类型，则对各操作数应用一般算术转换，然后
</p>
<ul><li> 若需要进行除了从整型类型到浮点类型之外的窄化转换，则程序非良构。
</li><li> 否则，若各操作数均具有整型类型，则运算符产出 <a href="../utility/compare/strong_ordering.html" title="cpp/utility/compare/strong ordering"><tt>std::strong_ordering</tt></a> 类型的纯右值：
</li></ul>
<dl><dd><ul><li> 若两个操作数算术上相等则为 <span class="t-lc">std::strong_ordering::equal</span>，
</li><li> 若第一操作数算术上小于第二个则为 <span class="t-lc">std::strong_ordering::less</span>
</li><li> 否则为 <span class="t-lc">std::strong_ordering::greater</span>。
</li></ul>
</dd></dl>
<ul><li> 否则，操作数均具有浮点类型，而运算符产出 <a href="../utility/compare/partial_ordering.html" title="cpp/utility/compare/partial ordering"><tt>std::partial_ordering</tt></a> 类型的纯右值。表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">&lt;=&gt;</span> b</span></span> 产出
</li></ul>
<dl><dd><ul><li> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">a</span></span> 小于 <span class="t-c"><span class="mw-geshi cpp source-cpp">b</span></span> 则为 <span class="t-lc">std::partial_ordering::less</span>
</li><li> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">a</span></span> 大于 <span class="t-c"><span class="mw-geshi cpp source-cpp">b</span></span> 则为 <span class="t-lc">std::partial_ordering::greater</span>
</li><li> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">a</span></span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">b</span></span> 则为 <span class="t-lc">std::partial_ordering::equivalent</span>（<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">0</span> <span class="sy1">&lt;=&gt;</span> <span class="sy2">+</span><span class="nu0">0</span></span></span> 为等价）
</li><li> 否则为 <span class="t-lc">std::partial_ordering::unordered</span>（<span class="t-c"><span class="mw-geshi cpp source-cpp">NaN <span class="sy1">&lt;=&gt;</span> 任何值</span></span> 为无序）
</li></ul>
</dd></dl>
<p>若两个操作数都具有相同的枚举类型 E，则运算符产出将各操作数转换为 E 的底层类型再对转换后的操作数应用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">&lt;=&gt;</span></span></span> 的结果。
</p><p>若至少一个操作数为指针或成员指针，则按需应用数组到指针转换、派生类到基类指针转换、函数指针转换和限定性转换，以将它们转换为同一指针类型，且结果指针类型为对象指针类型，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">p <span class="sy1">&lt;=&gt;</span> q</span></span> 返回 <a href="../utility/compare/strong_ordering.html" title="cpp/utility/compare/strong ordering"><tt>std::strong_ordering</tt></a> 类型的纯右值：
</p>
<ul><li> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">p <span class="sy1">==</span> q</span></span> 则为 <span class="t-lc">std::strong_ordering::equal</span>
</li><li> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">q <span class="sy1">&gt;</span> p</span></span> 则为 <span class="t-lc">std::strong_ordering::less</span>
</li><li> 若 <span class="t-c"><span class="mw-geshi cpp source-cpp">p <span class="sy1">&gt;</span> q</span></span> 则为 <span class="t-lc">std::strong_ordering::greater</span>。
</li><li> 若未指明这些指针值的比较（例如它们不指向同一对象或数组之中时），则为未指明的结果。
</li></ul>
<p>否则程序非良构。
</p><p>在<a href="overload_resolution.html#.E8.B0.83.E7.94.A8.E9.87.8D.E8.BD.BD.E8.BF.90.E7.AE.97.E7.AC.A6" title="cpp/language/overload resolution">针对用户定义运算符的重载决议</a>中，对于指针或枚举类型 <code>T</code>，下列函数签名参与重载决议：
</p>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td class="t-dcl-nopad"> <div><span class="mw-geshi cpp source-cpp">R operator<span class="sy1">&lt;=&gt;</span><span class="br0">(</span>T, T<span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad">  </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>其中 R 是上文所定义的排序类别类型。
</p>
<h3> <span class="mw-headline" id=".E6.B3.A8.E8.A7.A3_2">注解</span></h3>
<p>类类型可以自动生成三路比较，见<a href="default_comparisons.html" title="cpp/language/default comparisons">默认比较</a>。
</p><p>如果两个运算数均为数组，则除了比较数组类型的类成员之外，三路比较均为非良构。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">unsigned</span> <span class="kw4">int</span> i <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
<span class="kw4">auto</span> r <span class="sy1">=</span> <span class="sy2">-</span><span class="nu0">1</span> <span class="sy1">&lt;</span> i<span class="sy4">;</span> <span class="co1">// 既存陷阱：返回 false</span>
<span class="kw4">auto</span> r2 <span class="sy1">=</span> <span class="sy2">-</span><span class="nu0">1</span> <span class="sy1">&lt;=&gt;</span> i<span class="sy4">;</span> <span class="co1">// 错误：要求窄化转换</span></pre></div></div>
<p><br>
</p>
</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td></tr>
</table>
<h3><span class="mw-headline" id=".E6.A0.87.E5.87.86.E5.BA.93">标准库</span></h3>
<p>比较运算符为标准库中的许多类所重载。
</p>
<table class="t-dsc-begin">

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../types/type_info/operator_cmp.html" title="cpp/types/type info/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>  检查对象是否指代相同类型 <br> <span class="t-mark">(<code>std::type_info</code> 的公开成员函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../error/error_code/operator_cmp.html" title="cpp/error/error code/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>  比较两个 <code>error_code</code>  <br> <span class="t-mark">(函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../error/error_condition/operator_cmp.html" title="cpp/error/error condition/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   比较 <code>error_condition</code> 和 <code>error_code</code>  <br> <span class="t-mark">(函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../utility/pair/operator_cmp.html" title="cpp/utility/pair/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按字典序比较 pair 中的值  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../utility/tuple/operator_cmp.html" title="cpp/utility/tuple/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按字典顺序比较 tuple 中的值  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../utility/bitset/operator_cmp.html" title="cpp/utility/bitset/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较其内容  <br> <span class="t-mark">(<code>std::bitset&lt;N&gt;</code> 的公开成员函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../memory/allocator/operator_cmp.html" title="cpp/memory/allocator/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>  比较两个分配器实例  <br> <span class="t-mark">(<code>std::allocator&lt;T&gt;</code> 的公开成员函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../memory/unique_ptr/operator_cmp.html" title="cpp/memory/unique ptr/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span></span><span></span><span></span><span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   与另一个 <code>unique_ptr</code> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span> 进行比较  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../memory/shared_ptr/operator_cmp.html" title="cpp/memory/shared ptr/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   与另一个 <code>shared_ptr</code> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span> 进行比较  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../utility/functional/function/operator_cmp.html" title="cpp/utility/functional/function/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较 <span class="t-lc"><a href="../utility/functional/function.html" title="cpp/utility/functional/function">std::function</a></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span> <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../chrono/duration/operator_cmp.html" title="cpp/chrono/duration/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>  比较两个时长  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../chrono/time_point/operator_cmp.html" title="cpp/chrono/time point/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   比较两个时间点  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../memory/scoped_allocator_adaptor/operator_cmp.html" title="cpp/memory/scoped allocator adaptor/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>  比较两个 scoped_allocator_adaptor 实例 <br> <span class="t-mark">(<code>std::scoped_allocator_adaptor&lt;OuterAlloc,InnerAlloc...&gt;</code> 的公开成员函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../types/type_index/operator_cmp.html" title="cpp/types/type index/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span></span><span></span><span></span><span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>  比较底层 <span class="t-lc"><a href="../types/type_info.html" title="cpp/types/type info">std::type_info</a></span> 对象 <br> <span class="t-mark">(<code>std::type_index</code> 的公开成员函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../string/basic_string/operator_cmp.html" title="cpp/string/basic string/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&gt;</span><span>operator&lt;=</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>  以字典序比较两个字符串 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../locale/locale/operator_cmp.html" title="cpp/locale/locale/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   locale 对象之间的相等性比较  <br> <span class="t-mark">(<code>std::locale</code> 的公开成员函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/array/operator_cmp.html" title="cpp/container/array/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 array 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/deque/operator_cmp.html" title="cpp/container/deque/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 deque 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/forward_list/operator_cmp.html" title="cpp/container/forward list/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 forward_list 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/list/operator_cmp.html" title="cpp/container/list/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 list 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/vector/operator_cmp.html" title="cpp/container/vector/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 vector 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/map/operator_cmp.html" title="cpp/container/map/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 map 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/multimap/operator_cmp.html" title="cpp/container/multimap/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 multimap 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/set/operator_cmp.html" title="cpp/container/set/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 set 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/multiset/operator_cmp.html" title="cpp/container/multiset/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 multiset 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/unordered_map/operator_cmp.html" title="cpp/container/unordered map/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较 unordered_map 中的值  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/unordered_multimap/operator_cmp.html" title="cpp/container/unordered multimap/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较 unordered_multimap 中的值  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/unordered_set/operator_cmp.html" title="cpp/container/unordered set/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较 unordered_set 中的值  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/unordered_multiset/operator_cmp.html" title="cpp/container/unordered multiset/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较 unordered_multiset 中的值  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/queue/operator_cmp.html" title="cpp/container/queue/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 queue 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../container/stack/operator_cmp.html" title="cpp/container/stack/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   按照字典顺序比较 stack 中的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../iterator/reverse_iterator/operator_cmp.html" title="cpp/iterator/reverse iterator/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span></span><span></span><span></span><span></span><span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   比较底层迭代器  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../iterator/move_iterator/operator_cmp.html" title="cpp/iterator/move iterator/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span></span><span></span><span></span><span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   比较底层迭代器  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../iterator/istream_iterator/operator_cmp.html" title="cpp/iterator/istream iterator/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较两个 <code>istream_iterator</code>  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../iterator/istreambuf_iterator/operator_cmp.html" title="cpp/iterator/istreambuf iterator/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较两个 <code>istreambuf_iterator</code>  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../numeric/complex/operator_cmp.html" title="cpp/numeric/complex/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>  比较两个复数，或一个复数与一个标量  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../numeric/valarray/operator_cmp.html" title="cpp/numeric/valarray/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span></span></a></div></div>
</td>
<td>   比较两个 valarrays，或比较一个 valarray 和一个值  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../numeric/random/linear_congruential_engine/operator_cmp.html" title="cpp/numeric/random/linear congruential engine/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div></div>
</td>
<td>  比较两个伪随机数引擎的内部状态 <br> <span class="t-mark">(函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../numeric/random/poisson_distribution/operator_cmp.html" title="cpp/numeric/random/poisson distribution/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div></div>
</td>
<td>  比较两个分布对象 <br> <span class="t-mark">(函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../regex/sub_match/operator_cmp.html" title="cpp/regex/sub match/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span><span>operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   比较一个 <code>sub_match</code> 与另一 <code>sub_match</code> 、字符串或字符  <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../regex/match_results/operator_cmp.html" title="cpp/regex/match results/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>  以字典序比较两个匹配结果的值 <br> <span class="t-mark">(函数模板)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../regex/regex_iterator/operator_cmp.html" title="cpp/regex/regex iterator/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较两个 <code>regex_iterator</code>  <br> <span class="t-mark">(<code>std::regex_iterator&lt;BidirIt,CharT,Traits&gt;</code> 的公开成员函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../regex/regex_token_iterator/operator_cmp.html" title="cpp/regex/regex token iterator/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div></div>
</td>
<td>   比较两个 <code>regex_token_iterator</code>  <br> <span class="t-mark">(<code>std::regex_token_iterator&lt;BidirIt,CharT,Traits&gt;</code> 的公开成员函数)</span> </td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../thread/thread/id/operator_cmp.html" title="cpp/thread/thread/id/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt; </span><span> operator&lt;= </span><span> operator&gt; </span><span> operator&gt;= </span><span> operator&lt;=&gt;</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div>
</td>
<td>   比较两个 <code>thread::id</code> 对象  <br> <span class="t-mark">(函数)</span> </td></tr>
</table>
<p>命名空间 <a href="../utility/rel_ops/operator_cmp.html" title="cpp/utility/rel ops/operator cmp">rel_ops</a> 提供了泛型运算符 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span><span class="sy1">=</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">&gt;</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">&lt;=</span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy1">&gt;=</span></span></span>
</p>
<table class="t-dsc-begin">

<tr class="t-dsc-header">
<td colspan="2"> <div>定义于头文件 <code>&lt;utility&gt;</code> </div>
</td></tr>

<tr class="t-dsc-header">
<td colspan="2"> <div>定义于命名空间 <code>std::rel_ops</code></div>
</td></tr>

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="../utility/rel_ops/operator_cmp.html" title="cpp/utility/rel ops/operator cmp"> <span class="t-lines"><span>operator!=</span><span>operator&gt;</span><span>operator&lt;=</span><span>operator&gt;=</span></span></a></div><div><span class="t-lines"><span><span class="t-mark">(C++20 中弃用)</span></span></span></div></div>
</td>
<td>  自动生成基于用户定义的 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">==</span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">&lt;</span></span></span> 的比较运算符 <br> <span class="t-mark">(函数模板)</span> </td></tr>
</table>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<p><a href="operator_precedence.html" title="cpp/language/operator precedence">运算符优先级</a>
</p><p><a href="operators.html" title="cpp/language/operators">运算符重载</a>
</p>
<table class="wikitable">

<tr style="text-align:center">
<th colspan="7">常见运算符
</th></tr>
<tr style="text-align:center">
<td> <a href="operator_assignment.html" title="cpp/language/operator assignment">赋值</a>
</td>
<td> <a href="operator_incdec.html" title="cpp/language/operator incdec">自增<br>自减</a>
</td>
<td> <a href="operator_arithmetic.html" title="cpp/language/operator arithmetic">算术</a>
</td>
<td> <a href="operator_logical.html" title="cpp/language/operator logical">逻辑</a>
</td>
<td> <strong class="selflink">比较</strong>
</td>
<td> <a href="operator_member_access.html" title="cpp/language/operator member access">成员访问</a>
</td>
<td> <a href="operator_other.html" title="cpp/language/operator other">其他</a>
</td></tr>
<tr style="text-align:center">
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">=</span> b<br>
a <span class="sy2">+</span><span class="sy1">=</span> b<br>
a <span class="sy2">-</span><span class="sy1">=</span> b<br>
a <span class="sy2">*</span><span class="sy1">=</span> b<br>
a <span class="sy2">/</span><span class="sy1">=</span> b<br>
a <span class="sy2">%</span><span class="sy1">=</span> b<br>
a <span class="sy3">&amp;</span><span class="sy1">=</span> b<br>
a <span class="sy3">|</span><span class="sy1">=</span> b<br>
a <span class="sy3">^</span><span class="sy1">=</span> b<br>
a <span class="sy1">&lt;&lt;=</span> b<br>
a <span class="sy1">&gt;&gt;=</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>a<br>
<span class="sy2">--</span>a<br>
a<span class="sy2">++</span><br>
a<span class="sy2">--</span></span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">+</span>a<br>
<span class="sy2">-</span>a<br>
a <span class="sy2">+</span> b<br>
a <span class="sy2">-</span> b<br>
a <span class="sy2">*</span> b<br>
a <span class="sy2">/</span> b<br>
a <span class="sy2">%</span> b<br>
~a<br>
a <span class="sy3">&amp;</span> b<br>
a <span class="sy3">|</span> b<br>
a <span class="sy3">^</span> b<br>
a <span class="sy1">&lt;&lt;</span> b<br>
a <span class="sy1">&gt;&gt;</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span>a<br>
a <span class="sy3">&amp;&amp;</span> b<br>
a <span class="sy3">||</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">==</span> b<br>
a <span class="sy3">!</span><span class="sy1">=</span> b<br>
a <span class="sy1">&lt;</span> b<br>
a <span class="sy1">&gt;</span> b<br>
a <span class="sy1">&lt;=</span> b<br>
a <span class="sy1">&gt;=</span> b<br>
a <span class="sy1">&lt;=&gt;</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span>b<span class="br0">]</span><br>
<span class="sy2">*</span>a<br>
<span class="sy3">&amp;</span>a<br>
a<span class="sy2">-</span><span class="sy1">&gt;</span>b<br>
a.<span class="me1">b</span><br>
a<span class="sy2">-</span><span class="sy1">&gt;</span><span class="sy2">*</span>b<br>
a.<span class="sy2">*</span>b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">(</span>...<span class="br0">)</span><br>
a, b<br>
<span class="sy4">?</span> <span class="sy4">:</span></span></span>
</p>
</td></tr>
<tr>
<th colspan="7">特殊运算符
</th></tr>
<tr>
<td colspan="7">
<p><a href="static_cast.html" title="cpp/language/static cast"><tt>static_cast</tt></a> 转换一个类型为另一相关类型<br>
<a href="dynamic_cast.html" title="cpp/language/dynamic cast"><tt>dynamic_cast</tt></a> 在继承层级中转换<br>
<a href="const_cast.html" title="cpp/language/const cast"><tt>const_cast</tt></a> 添加或移除 <a href="cv.html" title="cpp/language/cv">cv</a> 限定符<br>
<a href="reinterpret_cast.html" title="cpp/language/reinterpret cast"><tt>reinterpret_cast</tt></a> 转换类型到无关类型<br>
<a href="explicit_cast.html" title="cpp/language/explicit cast">C 风格转型</a> 以 <code>static_cast</code> 、 <code>const_cast</code> 及 <code>reinterpret_cast</code> 的混合转换一个类型到另一类型<br>
<a href="new.html" title="cpp/language/new"><tt>new</tt></a> 创建有动态存储期的对象<br>
<a href="delete.html" title="cpp/language/delete"><tt>delete</tt></a> 销毁先前由 new 表达式创建的对象，并释放其所拥有的内存区域<br>
<a href="sizeof.html" title="cpp/language/sizeof"><tt>sizeof</tt></a> 查询类型的大小<br>
<a href="sizeof....html" title="cpp/language/sizeof..."><tt>sizeof...</tt></a> 查询<a href="parameter_pack.html" title="cpp/language/parameter pack">形参包</a>的大小<span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br>
<a href="typeid.html" title="cpp/language/typeid"><tt>typeid</tt></a> 查询类型的类型信息<br>
<a href="noexcept.html" title="cpp/language/noexcept"><tt>noexcept</tt></a> 查询表达式是否能抛出异常<span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br>
<a href="alignof.html" title="cpp/language/alignof"><tt>alignof</tt></a> 查询类型的对齐要求<span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td></tr></table>
<table class="t-dsc-begin">

</table>

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